Astable multivibrator using 555 Timer IC

Components Required:

1.  555 Timer IC & their datasheet (download here)
2. Resistor:- 1K, 1M, 100K.
3. Capacitor:- .1uF(104-Ceramic), 1uF or 2uF (Electrolytic)
4. 9V battery as a dc power source
5. Breadboard, Wires, LED.

Circuit description:

Astable multivibrator circuit

Here R3=470ohm or 1K for LED, C1=0.1uF or 0.01uF.

 

Practical Result:

LED ON time can be calculated using

T_high = 0.7*(R1+R2)*C2

LED OFF timing can be calculated using

T_low = 0.7*R2*C2

Total timing can  be calculated using

T = T_high+ T_low

Frequency can be calculated using
f = 1/T

  

555 Timer IC

The IC is made up of a combination of linear comparators and digital flip-flops. The entire circuit is usually housed in an 8-pin package.

555 IC Pin-out

Pin-out:

The connection of the pins for a DIP package is as follows:

Pin	Name	Purpose
1	GND	Ground reference voltage, low level (0 V)
2	TRIG	The OUT pin goes high and a timing interval starts when this input falls below 1/2 of CTRL voltage (which is typically 1/3 of VCC, when CTRL is open).
3	OUT	This output is driven to approximately 1.7 V below +VCC or GND.
4	RESET	A timing interval may be reset by driving this input to GND, but the timing does not begin again until RESET rises above approximately 0.7 volts. Overrides TRIG which overrides THR.
5	CTRL	Provides "control" access to the internal voltage divider (by default, 2/3 VCC).
6	THR	The timing (OUT high) interval ends when the voltage at THR is greater than that at CTRL (2/3 VCC if CTRL is open).
7	DIS	Open collector output which may discharge a capacitor between intervals. In phase with output.
8	VCC	Positive supply voltage, which is usually between 3 and 15 V depending on the variation.

How to identify NPN & PNP transistor?

1. Turn your multi-meter knob towards ‘diode’ mark, where we do short-circuit test.
   
2. Put Red color lead at Base of transistor and black at either side.
   
   If there is any deflection, then the transistor you are tested, that is N-P-N transistor.
   
3. Put Black color lead at Base of transistor and Red at either side.
   
   If there is any deflection, then the transistor you are tested, that is P-N-P transistor.